diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5fcce16e9c..fbd503e3c8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,15 @@ develop
 
 
 
+3.1.5
+--------------------------
+
+### Fixes
+
+- Fix an issue where the application could crash by auto-completion on OS X 10.10.
+
+
+
 3.1.4 (182)
 --------------------------
 
diff --git a/CotEditor/CotEditor -AppStore-Info.plist b/CotEditor/CotEditor -AppStore-Info.plist
index 36f51756b9..b2781396b8 100644
--- a/CotEditor/CotEditor -AppStore-Info.plist	
+++ b/CotEditor/CotEditor -AppStore-Info.plist	
@@ -945,11 +945,11 @@
 	<key>CFBundlePackageType</key>
 	<string>APPL</string>
 	<key>CFBundleShortVersionString</key>
-	<string>3.1.4</string>
+	<string>3.1.5</string>
 	<key>CFBundleSignature</key>
 	<string>cEd1</string>
 	<key>CFBundleVersion</key>
-	<string>182</string>
+	<string>184</string>
 	<key>LSApplicationCategoryType</key>
 	<string>public.app-category.productivity</string>
 	<key>LSMinimumSystemVersion</key>
diff --git a/CotEditor/CotEditor-Info.plist b/CotEditor/CotEditor-Info.plist
index 1e02acd343..94d4930ff5 100644
--- a/CotEditor/CotEditor-Info.plist
+++ b/CotEditor/CotEditor-Info.plist
@@ -945,11 +945,11 @@
 	<key>CFBundlePackageType</key>
 	<string>APPL</string>
 	<key>CFBundleShortVersionString</key>
-	<string>3.1.4</string>
+	<string>3.1.5</string>
 	<key>CFBundleSignature</key>
 	<string>cEd1</string>
 	<key>CFBundleVersion</key>
-	<string>182</string>
+	<string>184</string>
 	<key>LSApplicationCategoryType</key>
 	<string>public.app-category.productivity</string>
 	<key>LSMinimumSystemVersion</key>
diff --git a/CotEditor/CotEditor.help/Contents/Resources/en.lproj/pgs/releasenotes.html b/CotEditor/CotEditor.help/Contents/Resources/en.lproj/pgs/releasenotes.html
index 1fd69928a9..0e4641f04a 100644
--- a/CotEditor/CotEditor.help/Contents/Resources/en.lproj/pgs/releasenotes.html
+++ b/CotEditor/CotEditor.help/Contents/Resources/en.lproj/pgs/releasenotes.html
@@ -22,16 +22,27 @@
 <h1>Release Notes</h1>
 
 
-<!-- 	<li>Now, AppleScript's script bundles can specify execution mode to enable running the script inside the application Sandbox (thanks to Kaito Udagawa!).
-	<ul>
-		<li>See <a href="about_script_hook.html">Adding scripting hooks for CotEditor scripts</a> from the Help menu &gt; CotEditor Scripting Manual &gt; <a href="about_scripting.html">About Scripting</a> for details.</li>
-		</ul></li> -->
+<article>
+<header>
+	<h1>CotEditor 3.1.5</h1>
+	<p>release: <time>2016-02</time></p>
+</header>
+
+
+<section>
+<h3>Fixes</h3>
+
+<ul>
+	<li>Fix an issue where the application could crash by auto-completion on OS X 10.10.</li>
+</ul>
+</section>
+</article>
 
 
 <article>
 <header>
 	<h1>CotEditor 3.1.4</h1>
-	<p>release: <time>2016-02</time></p>
+	<p>release: <time>2016-02-20</time></p>
 </header>
 
 
diff --git a/CotEditor/CotEditor.help/Contents/Resources/ja.lproj/pgs/releasenotes.html b/CotEditor/CotEditor.help/Contents/Resources/ja.lproj/pgs/releasenotes.html
index 595680c302..466e3f223b 100644
--- a/CotEditor/CotEditor.help/Contents/Resources/ja.lproj/pgs/releasenotes.html
+++ b/CotEditor/CotEditor.help/Contents/Resources/ja.lproj/pgs/releasenotes.html
@@ -24,11 +24,28 @@ <h1>リリースノート</h1>
 
 <article>
 <header>
-	<h1>CotEditor 3.1.4</h1>
+	<h1>CotEditor 3.1.5</h1>
 	<p>リリース: <time>2016-02</time></p>
 </header>
 
 
+<section>
+<h2>修正</h2>
+
+<ul>
+	<li>OS X 10.10 で自動補完をするとアプリケーションアイコンがクラッシュすることがある不具合を修正</li>
+</ul>
+</section>
+</article>
+
+
+<article>
+<header>
+	<h1>CotEditor 3.1.4</h1>
+	<p>リリース: <time>2016-02-20</time></p>
+</header>
+
+
 <section>
 <h2>新機能</h2>
 
diff --git a/CotEditor/Sources/EditorTextView.swift b/CotEditor/Sources/EditorTextView.swift
index b400af7b5c..686a32ae3c 100644
--- a/CotEditor/Sources/EditorTextView.swift
+++ b/CotEditor/Sources/EditorTextView.swift
@@ -67,7 +67,9 @@ final class EditorTextView: NSTextView, Themable {
     var initialMagnificationScale: CGFloat = 0
     var deferredMagnification: CGFloat = 0
     
-    private(set) lazy var completionTask: Debouncer = Debouncer { [weak self] in self?.performCompletion() }
+    private(set) lazy var completionTask: Debouncer = Debouncer { [weak container = self.textContainer] in  // NSTextView cannot be weak
+        (container?.textView as? EditorTextView)?.performCompletion()
+    }
     
     
     // MARK: Private Properties
diff --git a/CotEditor/Sources/SyntaxManager.swift b/CotEditor/Sources/SyntaxManager.swift
index 5ccd4073c1..0be05d7b2e 100644
--- a/CotEditor/Sources/SyntaxManager.swift
+++ b/CotEditor/Sources/SyntaxManager.swift
@@ -256,7 +256,7 @@ final class SyntaxManager: SettingFileManager {
         
         // load from file
         if let url = self.urlForUsedSetting(name: name),
-            let style = self.styleDictionary(fileURL: url) {
+            let style = try? self.styleDictionary(fileURL: url) {
             
             // store newly loaded style
             self.styleCaches[name] = style
@@ -273,7 +273,7 @@ final class SyntaxManager: SettingFileManager {
         
         guard let url = self.urlForBundledSetting(name: name) else { return nil }
         
-        return self.styleDictionary(fileURL: url)
+        return try? self.styleDictionary(fileURL: url)
     }
     
     
@@ -412,15 +412,21 @@ final class SyntaxManager: SettingFileManager {
     
     // MARK: Private Methods
     
-    /// return style dictionary at file URL
-    private func styleDictionary(fileURL: URL) -> StyleDictionary? {
+    /// Return style dictionary at file URL.
+    ///
+    /// - parameter fileURL: URL to a style file.
+    /// - throws: CocoaError
+    private func styleDictionary(fileURL: URL) throws -> StyleDictionary {
         
-        guard
-            let yamlData = try? Data(contentsOf: fileURL),
-            let yaml = try? YAMLSerialization.object(withYAMLData: yamlData,
-                                                     options: kYAMLReadOptionMutableContainersAndLeaves) else { return nil }
+        let yamlData = try Data(contentsOf: fileURL)
+        let yaml = try YAMLSerialization.object(withYAMLData: yamlData,
+                                                 options: kYAMLReadOptionMutableContainersAndLeaves)
+        
+        guard let styleDictionary = yaml as? StyleDictionary else {
+            throw CocoaError(.fileReadCorruptFile)
+        }
         
-        return yaml as? StyleDictionary
+        return styleDictionary
     }
     
     
@@ -459,14 +465,14 @@ final class SyntaxManager: SettingFileManager {
         let directoryURL = self.userSettingDirectoryURL
         var map = self.bundledMap
         
-        // load user styles
+        // load user styles if exists
         if let enumerator = FileManager.default.enumerator(at: directoryURL, includingPropertiesForKeys: nil,
                                                            options: [.skipsSubdirectoryDescendants, .skipsHiddenFiles]) {
             for case let url as URL in enumerator {
                 guard [self.filePathExtension, "yml"].contains(url.pathExtension) else { continue }
+                guard let style = try? self.styleDictionary(fileURL: url) else { continue }
                 
                 let styleName = self.settingName(from: url)
-                guard let style = self.styleDictionary(fileURL: url) else { continue }
                 
                 map[styleName] = [SyntaxKey.extensions.rawValue: type(of: self).keyStrings(in: style, key: .extensions),
                                   SyntaxKey.filenames.rawValue: type(of: self).keyStrings(in: style, key: .filenames),
diff --git a/CotEditor/Sources/ThemeManager.swift b/CotEditor/Sources/ThemeManager.swift
index 0829625f87..d971f0424e 100644
--- a/CotEditor/Sources/ThemeManager.swift
+++ b/CotEditor/Sources/ThemeManager.swift
@@ -9,7 +9,7 @@
  
  ------------------------------------------------------------------------------
  
- © 2014-2016 1024jp
+ © 2014-2017 1024jp
  
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
@@ -246,12 +246,20 @@ final class ThemeManager: SettingFileManager {
     
     // MARK: Private Methods
     
-    /// create ThemeDictionary from a file at the URL
-    private func themeDictionary(fileURL: URL) -> ThemeDictionary? {
+    /// Create ThemeDictionary from a file at the URL.
+    ///
+    /// - parameter fileURL: URL to a theme file.
+    /// - throws: CocoaError
+    private func themeDictionary(fileURL: URL) throws -> ThemeDictionary {
         
-        guard let data = try? Data(contentsOf: fileURL) else { return nil }
+        let data = try Data(contentsOf: fileURL)
+        let json = try JSONSerialization.jsonObject(with: data, options: .mutableContainers)
         
-        return (try? JSONSerialization.jsonObject(with: data, options: .mutableContainers)) as? ThemeDictionary
+        guard let themeDictionry = json as? ThemeDictionary else {
+            throw CocoaError(.fileReadCorruptFile)
+        }
+        
+        return themeDictionry
     }
     
     
@@ -265,9 +273,8 @@ final class ThemeManager: SettingFileManager {
             let themeNameSet = NSMutableOrderedSet(array: strongSelf.bundledThemeNames)
             
             // load user themes if exists
-            if userDirURL.isReachable {
-                let fileURLs = (try? FileManager.default.contentsOfDirectory(at: userDirURL, includingPropertiesForKeys: nil,
-                                                                            options: [.skipsSubdirectoryDescendants, .skipsHiddenFiles])) ?? []
+            if let fileURLs = try? FileManager.default.contentsOfDirectory(at: userDirURL, includingPropertiesForKeys: nil,
+                                                                           options: [.skipsSubdirectoryDescendants, .skipsHiddenFiles]) {
                 let userThemeNames = fileURLs
                     .filter { $0.pathExtension == strongSelf.filePathExtension }
                     .map { strongSelf.settingName(from: $0) }
@@ -280,10 +287,13 @@ final class ThemeManager: SettingFileManager {
             
             // cache definitions
             strongSelf.archivedThemes = (themeNameSet.array as! [String]).reduce([:]) { (dict, name) in
-                guard let themeURL = strongSelf.urlForUsedSetting(name: name) else { return dict }
+                guard
+                    let themeURL = strongSelf.urlForUsedSetting(name: name),
+                    let themeDictionary = try? strongSelf.themeDictionary(fileURL: themeURL)
+                    else { return dict }
                 
                 var dict = dict
-                dict[name] = strongSelf.themeDictionary(fileURL: themeURL)
+                dict[name] = themeDictionary
                 return dict
             }
             
@@ -310,7 +320,7 @@ final class ThemeManager: SettingFileManager {
         
         let url = self.urlForBundledSetting(name: "_Plain")!
         
-        return self.themeDictionary(fileURL: url)!
+        return try! self.themeDictionary(fileURL: url)
     }
     
 }